1. Field of the Invention
The present invention relates generally to projection display systems. More particularly, the present invention relates to a projection display system employing one or more electrically switchable holographic optical elements (ESHOEs).
2. Description of the Related Art
Projection display systems operate to display an image or a sequence of images onto a screen. Projection displays can be employed in numerous systems. For example, projection displays can be employed to display images created by a laptop or desktop computer systems.
Projection systems typically include a projector and a screen for receiving projected images from the projector. The projector and the screen may operate to display a color image formed, for example, by projecting three monochromatic image components of the color image onto the screen. The projector may comprised of an image generator and projection optics. The image generator may contain a light source that provides white illumination light to an input image display panel. As an example, the input image display panel may be a reflective liquid crystal display (LCD) panel which is illuminated by the light from the light source. The display panel generates the image components that are to be projected onto the screen.
The present invention relates to an optical system for use in a projection display system. The optical system, in one embodiment, includes a first electrically switchable holographic optical element (ESHOE) and a light deflector. The first ESHOE operates between active and inactive states and includes oppositely facing front and back surfaces. In the inactive state, the first ESHOE transmits first bandwidth light received on the front surface without substantial alteration. In the active state, the first ESHOE diffracts first bandwidth light received on the front surface, the diffracted first bandwidth light emerging also from the front surface. The light deflector receives first bandwidth light diffracted by the first ESHOE. In response, the light deflector deflects this diffracted first bandwidth light. The first ESHOE and the light deflector are positioned such that first bandwidth light transmitted through the inactive first ESHOE without substantial alteration can illuminate a first surface area while first bandwidth light diffracted by the active first ESHOE and subsequently deflected by the light deflector can illuminate a second non-overlapping.
The projection display system employing the optical system described above, can also include an image generator (also known as an input image display panel) and a display screen. The image generator may take form in any one of several arrangements. For example, the image generator could be any type of high light output display such as a color sequentially illuminated reflective LCD. Alternatively, the image display may include a set of three separately illuminated red, green, and blue reflective LCD display panels. Employing a set of three separately illuminated red, green, and blue reflective LCD display panels is advantageous in that it avoids the problem of color break up and provides better light throughput than a single LCD image generator. Further, the image generator may take form in one or more laser scanning devices which output one or more laser beams modulated in accordance with a sequence of image signals. These modulated laser beams scan a display surface area in raster like fashion when displaying an image frame. The display screen may include first and second panels which include the first and second surface areas, respectively, mentioned above. The display panels may be capable of rotation around a common axis.
In another embodiment, the optical system may include second and third ESHOEs in communication with the first ESHOE. The second and third ESHOEs may include oppositely facing front and back surfaces. Like the first ESHOE, the second and third ESHOEs operate between active and inactive states. In the active state, the second and third ESHOEs transmit second and third bandwidth light, respectively, received on their respective front surfaces. The second and third ESHOEs transmit second and third bandwidth light, respectively, without substantial alteration while operating in the inactive state. The second and third ESHOEs diffract second and third bandwidth light, respectively, received on a respective front surfaces when operating in the active state. In contrast to the inactive mode, second and third bandwidth light received and diffracted by the second and third ESHOEs, respectively, emerge from respective front surfaces thereof.
The light deflector may be positioned to receive the second and third bandwidth lights diffracted by the second and third ESHOEs, respectively. The light deflector may be configured to deflect the second and third bandwidth lights onto the second surface area. Further, second and third bandwidth lights transmitted through inactive second and third ESHOEs, respectively, without substantial alteration, can illuminate the first surface area.
The light deflector may take form in any one of several embodiments including a conventional mirror, a static holographic optical element, or an ESHOE. The light deflector embodied within an ESHOE operates between active and inactive states. In the active state, ESHOE diffracts one or more different bandwidths of visible light. In the inactive state, this ESHOE transmits substantially all light incident thereon without substantial alteration.